Silica (SiO.sub.2) films are of great interest to the semiconductor, optical and other industries. The silica films can be prepared by several methods such as thermal oxidation, physical vapor deposition, thermal vapor deposition, chemical vapor deposition and spin-on glass (SOG) technology.
The SOG materials are organsilicon polymers that can be synthesized by the hydrolysis of various silanes. There are two types of SOG materials such as p-SOG materials and s-SOG materials. The p-SOG materials are essentially polysiloxanes with inert organic groups such as methyl, ethyl, phenyl, etc. The s-SOG materials are basically silicate-like materials with reactive side chains such as hydroxyl, methoxy, ethoxy, etc. These silicone or silicate materials generally are only capable of making silica films with a thickness of less than 1 micrometer or otherwise cracking results during the steps of heating or oxygen plasma treatment.
In order to solve this problem, new types of carboxylated polysiloxanes have been synthesized. These new carboxylated polysiloxanes exhibit improved abilities to form silica and silicate films.
An additional advantage of the new carboxylated polysiloxanes is that their carboxyl groups can be ion-exchanged by metal ions to form metal doped polysiloxane films. These films can be transformed into metal doped silicate films through thermal oxidation or other means.
The further advantage of the new carboxylated polysiloxane compositions is that methyl groups or vinyl groups in the materials, when spread on substrates, can be used for cross-linking (such as by photolytic crosslinking) to form insoluble siloxane films or patterns in the shape of the image made by the photolysis source. This source can be light passed through a mask or light of a laser beam directed to specified regions of the material. After removal of uncrosslinked material, the crosslinked, carboxylated silicone patterns then can be ion-exchanged with metal ions, such as alkali, alkaline earth, transition metal, and rare earth metal ions to form metal-doped siloxane patterns. The metal doped polysiloxane patterns can then in turn be oxidized into metal silicate patterns which can be used as waveguide structures and optical, electrooptical, or magneto-optical devices.
In this regard, in the planar waveguide structures, a higher refractive index often is needed in the guided region than that of its cladding. One known way to achieve such an index step is to exchange some of the cations in a sodium borosilicate glass. The exchange process is started by masking off the area where the index is to be left unchanged. A metal salt such as silver iodide is painted over the surface of the planar waveguide blank. The blank is then heated to 300.degree. C. to 400.degree. C. where ion exchange takes place (diffusion of the sodium out and silver in). After being cooled, the planar waveguide is ground and polished to allow coupling into optical systems.
Waveguide structures also can be produced by laser densification of sol-gel silica glass. For normal glass, there would be no densification effect upon laser heating or heat treatments by other means. With sol-gel silica, partially dense type VI silica can be used as a substrate. Upon laser heating, the region under the focused beam is densified. This will form a multimode waveguide region of 40 .mu.m wide with a refractive index difference of 0.06 between the waveguided region and the substrate.
In the preparation of a waveguide structure through a sol-gel method, ethanol, HCl/water, germanium ethoxide (Ge(OC.sub.2 H.sub.5).sub.4) and tetraethylorthosilicate (TEOS) are mixed together to form multi-component sol. Substrates are dip coated with the sol, and coatings are fired after every 10-12 dippings. The film is heated in the temperature range of 300-1100.degree. C. and densified at the temperature 850-1100.degree. C. The film is found to be of high optical quality.
Moreover, it often is desirous to have a region, such as a layer, whose refractive index is higher than that of the lightguided region, so it will be advantageous to produce germanium containing SOG materials which will be used to form germanosilicate films for waveguide applications. The present invention is directed to this objective and others. Specifically, one object of the invention to use germanium containing silicone compositions to formgermanosilicate films and multilayers for construction of waveguide structures.
These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following specification and drawings.